Synergetic Catalysis Of P-d Hybridized Single-atom Catalysts: First-principles Investigations

Single-atom catalysts（SACs）have triggered wide interest in heterogeneous catalysis due to their high catalytic efficiency and selectivity for many important chemical processes.Currently,the prevailing catalysts are d-block based noble metals such as Pt and Pd-based SACs fabricated with the TM-SA active centers being stabilized on the defective surfaces,step edges and alloys,nevertheless expensive and scare for broad commercial applications.Recently,nonmetal-based SACs with the p-block elements serving as the active sites have been attracted much attention in some important catalytic processes,benefiting from the relatively low cost,simple synthesis methods,and low toxic features.However,the delocalized electronic feature of the non-local p orbitals results in extra difficulties in precisely identifying the specific active site to understanding the underlying reaction mechanism.Therefore,it is of great theoretical significance and practical application to design SACs with atomically dispersed d-block catalytic sites periodically confined within the p-block element benefitting from both merits of d-block and p-block elemental SACs,yet to date only scattered efforts have been devoted to this field.In this thesis,we propose a new design principle,namely,p-d hybridized single-atom catalysts（p-d-HSACs）.Taking two-dimensional metal-organic frameworks（2D-MOFs）material TM₃（C₆O₆）₂ structure with high density and exposed d-block TM nodes and p-block elements as a p-d-HSAC candidate to precisely explore the synergistic interaction between p-and d-block elements in a specific chemical reaction.Based on density functional theory（DFT）calculations,taking CO oxidation reaction as a prototypical example,we find that an interesting p-d synergistic charge transfer mechanism exists in the TM₃（C₆O₆）₂ p-d-HSAC candidate system during O₂ activation and CO oxidation processes,which can effectively reduce the CO oxidization barriers to the range of 0.23～0.56 e V.The results demonstrate that the design of p-d-HSAC proposed in this study provides important theoretical guidance for the fabrication of economical and efficient SAC systems.The specific research content is organized as follows:We firstly investigates the properties related to the two-dimensional TM₃（C₆O₆）₂system with different d-block TM nodes,including geometric structure and stability.Firstly,taking experimentally synthesized Cu₃（C₆O₆）₂ and Ni₃（C₆O₆）₂ as benchmarks,the geometric configurations of thirteen different monolayer systems with formula TM₃（C₆O₆）₂（TM=Cr,Mn,Fe,Co,Ni,Cu,Mo,Ru,Rh,Pd,Ag,Pt,Au）were simulated and calculated,among which nine of them（TM=Cr,Mn,Fe,Co,Ni,Cu,Mo,Ru,Rh）were found to be energetically stable and were predicted to be candidates for p-d-HSACs.Based on the above candidate systems,the catalytic effect of the TM₃（C₆O₆）₂monolayer structure on the CO oxidation reaction was further simulated and studied using the first-principles calculations.Firstly,we investigated the adsorption of O₂ and CO molecules on TM sites in TM₃（C₆O₆）₂ and classified the 9 catalysts into three categories according to their respective adsorption energy and adsorption configuration:（I）O₂ molecules adsorbed laterally on TM sites,with distal O weakly adsorbed with the next closest neighboring C atom;（II）O₂ molecules physically adsorbed on the C₂O₂TM pentagonal hollow structure;and（III）O₂ molecules adsorbed endwise on TM sites.Based on these three types of configurations,we respectively investigated the reaction mechanism of CO oxidation reactions on these nine TM₃（C₆O₆）₂SACs candidate systems.It was found that during reactions that occur in these three classes,except for the hosting d-block TM active sites,the second-nearest neighboring p-block C atoms also dominate or donate significant charge via the bridge of the nearest neighboring substrate O atoms.which effectively reduces the CO oxidation barriers to the range of 0.23～0.56 e V.In this thesis,an intriguing p-d synergistic charge transfer mechanism is proposed for O₂ activation and CO oxidation using a TM₃（C₆O₆）₂ SACs candidate system with abundant d-block TM nodes and p-block elements,and it is found that p-d hybridization can improve the catalytic performance of CO oxidation.The results of this study provide theoretical guidance for the design of highly efficient and low-cost p-d-hybridized SAC systems.